How ultra-magnetized Kelvin-Helmholtz drag impacts precursor emission in neutron star binaries

Multi-messenger signals from binary neutron star (BNS) mergers are a unique window into the physics of compact objects and their magnetized environment. It is still unclear how the interacting magnetospheres of orbiting BNSs generate electromagnetic counterparts foreshadowing their final in-spiral. As one possible scenario, we explore the Kelvin-Helmholtz (KH) instability in the ultra-magnetized interaction layer between synchronized binary companions. In first-of-a-kind simulations, the drag generated by magnetospheric mixing in KH vortices dissipates significant electromagnetic energy: up to 40% of the spin-down luminosity. In addition, compressive plasma waves can develop shocks and become sources of fast radio bursts. Companions with inclined dipoles can mix KH episodes with flaring events. Then, the winding of magnetic field lines linking the two stars drives powerful coronal mass ejections similar to BNS merger flares.